Certain saw blades, such as bandsaw blades, are commonly made with recurring variations in the shape, spacing, height, and setting of the teeth, as well as in the width of the saw blade body. By "setting" or "set" it is meant that certain teeth or portions of certain teeth slant to the left or right of a centerline of the blade. Most of these variations serve to improve the properties of the blade for certain specific applications. However, the same variations often decrease the usefulness of the blade for other applications.
Bandsawing, especially bandsawing metal, presents problems not commonly encountered in other sawing methods. The bandsaw blade is usually made thin and narrow, which limits the total feed force that can be applied to force the teeth into the sawn material and makes the blade very flexible. To get a smooth cut, several teeth must be actively engaged in cutting simultaneously, which allows only a relatively small feed force for each of the teeth. Small feed force leads to small cutting depth which, especially for tough materials, means unstable chip formation and excessive wear. Further, the fewer the number of teeth that are actively engaged in cutting simultaneously, the greater the effect of the sudden change in tension when a tooth leaves or enters the cut, and problems associated with self-induced vibrations of the saw blade vertically, laterally, or torsionally may occur. For example, such vibrations tend to lead to uneven cut surfaces and noise.
Variations in tooth shape, especially edge shape, may serve to make the teeth cut several narrow and thick chips rather than fewer thin and wide chips. Formation of numerous narrow and thick chips leads to less wear, less friction against the cut sides, and, usually, better lateral stability than formation of fewer thin and wide chips. However, many blades having teeth with variations in shape require extra manufacturing operations and are, in consequence, expensive to make, or if desired, to resharpen.
Variations in tooth spacing can lower the tendency of self-induced chatter vibrations when sawing thick material, and tends to minimize noise from the sawing operation. There is, however, a tendency for teeth with variations in spacing to become unevenly worn, which may later contribute to transverse forces and crooked cutting.
Tooth height may be varied in various ways to serve different purposes. If straight teeth are longer than others, their side faces tend to guide the blade and produce a straight and narrow cut. However, straight teeth are unlikely to straighten a cut if it starts to veer to one side. If high straight teeth are combined with teeth having variations in setting, multiple narrow thick chips will be cut instead of fewer thin wide chips. This tends to improve the sawing of tough materials, but may leave uneven sides of the cut since only those few teeth set to maximum width shape the final cut surface. In tough material, the combination of high straight teeth and teeth with variations in setting may also be used at slow feed rates so that the high teeth perform the bulk of the actual cutting operation, thus minimizing unstable conditions at small cutting depths. In more easily cut materials, higher feed rates can be used so that the high straight teeth and the teeth with variations in setting are all engaged in cutting. Thus, such a blade is useful for a variety of materials, albeit with a risk of premature wear of the high teeth if much of the work is with tough materials.
It is an object of the present invention to provide a saw blade that may be used for cutting a great variety of materials. It is also an object of the present invention to provide a saw blade that is subject to only limited premature wear. It is also an object of the present invention to provide a tooth setting pattern that is able to produce very smooth cut surfaces.
According to one aspect of the present invention, a saw blade includes a plurality of recurring groups of teeth, each tooth having a point. Each group comprises one high straight tooth without set, an even number of high set teeth with points at a first level, half of the high set teeth being set to the right and half to the left, an even number, greater than the number of high set teeth, of low set teeth with points at a second level lower than the first level, half of the low set teeth being set to the right and half to the left. Points of each tooth in the group are at a different distance from a point of a corresponding, immediately preceding tooth. All set teeth in the group have the same amount of set. No high tooth is immediately preceded by another high tooth. There are an odd number of low teeth between a high straight tooth and a high set tooth, and there are an even number of low teeth between two set high teeth. Distances from a point of any tooth in the group to a point of a preceding tooth of the same height are different for all teeth in the group. Distances from a point of any set tooth in the group to a point of a preceding set tooth of the same set are different for all set teeth in the group.
Improvements in vibration and stability available with the saw blade according to the present invention are most pronounced in metal bandsaws, where the feed force of the saw blade is high in relation to the blade tension, however, the present invention is also applicable to other types of saw blades, such as hand hacksaws, wood bandsaws, and bow saws.